Portable pressure transducer, pneumotach for use therewith, and associated methods

ABSTRACT

A system for sensing respiratory pressure includes a portable pressure transducer configured to be carried by or proximate to a respiratory conduit, such as a breathing circuit or a nasal canula. The portable pressure transducer may removably couple with a pneumotach, in the form of an airway adapter, disposed along the respiratory conduit. The pneumotach may include two pressure ports positioned at opposite sides of an obstruction, which partially blocks flow through a primary conduit of the pneumotach. Corresponding sample conduits of the portable pressure transducer removably couple with the pressure ports. The pressure ports may have sealing elements which are configured to seal against piercing members of the sample conduits upon introduction of the piercing members therethrough. Upon removal of the piercing members, the sealing elements substantially reseal. Methods for using the system are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

Under the provisions of 35 U.S.C. §119(e), this application claims thebenefit of U.S. Provisional Application Serial No. 60/289,540, filed onMay 7, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to apparatus for measuringrespiratory pressure or flow and, more specifically, to respiratorypressure transducers. More particularly, the present invention relatesto pressure transducers which may be positioned proximate to arespiratory conduit which is configured to communicate with the airwayof an individual.

2. Background of Related Art

Respiratory flow measurement during the administration of anesthesia, inintensive care environments, and in monitoring the physical condition ofathletes and other individuals prior to and during the course oftraining programs and other medical tests provides valuable informationfor assessment of cardiopulmonary function and breathing circuitintegrity. Many different technologies have been applied to create aflow meter that attempts to meet the demanding requirements of theseenvironments.

Although various other types of pressure measurement apparatus areknown, differential pressure flow meters have conventionally been usedto obtain respiratory flow measurements. While pressure monitoring istypically performed to measure delivered (i.e., inspired) and exhaledvolume by monitoring respiratory mechanics parameters, such as airwaypressures, flow rates, and breath volumes, clinicians can better providequality health care to patients requiring breathing assistance.Additionally, pressure monitoring may be used in conjunction withrespiratory gas measurements to assess other respiratory parameters,such as oxygen consumption, carbon dioxide elimination, and even cardiacoutput or pulmonary capillary blood flow.

Differential pressure flow meters operate on the basis of Bernoulli'sprinciple: the pressure drop across a restriction is proportional to thevolumetric flow rate of the air. The relationship between flow and thepressure drop across a restriction or other resistance to flow isdependent upon the design of the resistance. In some differentialpressure flow meters, which are commonly termed “pneumotachs”, the flowrestriction has been designed to create a linear relationship betweenflow and a pressure differential. Such designs include the Fleischpneumotach, in which the restriction is comprised of many small tubes ora fine screen to ensure laminar flow and a more linear response to flow.Another physical configuration is a flow restriction having an orificethat varies in relation to the flow. Such designs include the variableorifice, fixed orifice and venturi-type flow meters. Exemplary patentsfor variable orifice differential pressure flow sensors include U.S.Pat. No. 4,993,269, issued to Guillaume et al. on Feb. 19, 1991, U.S.Pat. No. 5,038,621, issued to Stupecky on Aug. 13, 1991, U.S. Pat. No.5,763,792, issued to Kullik on Jun. 9, 1998, and U.S. Pat. No.5,970,801, issued to Ciobanu on Oct. 26, 1999. Exemplary patents forfixed orifice differential pressure flow sensors include U.S. Pat. No.5,379,650, issued to Kofoed et al. on Jan. 10, 1995, U.S. Pat. No.5,925,831, issued to Storsved on Jul. 20, 1999, and U.S. Pat. No.6,203,502, issued to Hilgendorf on Mar. 20, 2001.

Many known differential pressure flow sensors suffer deficiencies whenexposed to less than ideal gas and flow inlet conditions and, further,possess inherent design problems with respect to their ability to sensedifferential pressure in a meaningful, accurate, repeatable manner overa substantially dynamic flow range. This is particularly true when theflow sensor is needed to reliably and accurately measure low flow rates,such as the respiratory flow rates of infants. Proximal flow measured atthe patient's airway can be substantially different from flow measuredinside or at the ventilator. Many ventilators measure flow, not at theproximal airway, but close to the ventilator. Measurements of flow inthis way may result in a substantial difference between the flow,pressure, and volume of gases that are delivered to or exhaled by thepatient and that are reported by a pressure or flow sensor which isassociated with the ventilator. At least a portion of this discrepancyis because of wasted compression volume, which distends and may elongatea length of respiratory conduit positioned between the patient's airwayand the pressure or flow sensor, and humidification or dehumidificationattributable to the length of the respiratory conduit between thepatient's airway and the pressure or flow sensor. As the compliance ofthe respiratory conduit may be a known value, some ventilatormanufacturers apply a correction for the wasted compression volume. Evenwhen a correction is applied, precise estimation of the wasted andinhaled portions of the compression volume is difficult because ofvariations between individual respiratory conduits, the use ofhumidifiers, the use of heat-moisture exchangers, and other circuitcomponents. Within a typical respiratory conduit, gas conditions (e.g.,temperature, pressure, humidity, etc.) may vary considerably, dependingupon the distance of the gases from the airway of the monitoredindividual. As gas conditions nearest the individual are most likely toreflect the corresponding conditions within the individual's airway, thepreferred location for monitoring inspiratory and expiratory flows froma patient in the critical care environment is proximal (i.e., as closeto the individual's airway as possible).

Routine clinical use of differential flow meters has increasedsignificantly in the last few years with the development of more robustdesigns, such as that disclosed in U.S. Pat. No. 5,379,650, issued toKofoed et al. on Jan. 10, 1995 (hereinafter “the '650 patent”), thedisclosure of which is hereby incorporated herein in its entirety bythis reference. The differential flow meter described in the '650patent, which has overcome the majority of the problems that werepreviously encountered when prior differential pressure flow sensorswere used, includes a tubular housing containing a diametricallyoriented, longitudinally extending strut. The strut of the flow sensordisclosed in the '650 patent includes first and second lumens withlongitudinally spaced pressure ports that open into respective axiallylocated notches formed at each end of the strut.

Despite such improvements in the performance of differential pressureflow meters, differential pressure flow meters continue to include apneumotach positioned along a respiratory conduit, a typically remotelypositioned pressure monitor, and tubing that operatively connects thepneumotach and the pressure monitor with one another. The tubingtransmits pressure at each port of the pneumotach to one or morepressure sensors that are contained within the monitor. Typically,several feet of flexible, small bore, dual or triple lumen tubing areused to connect the pneumotach and the pressure monitor to one another.

The use of such small bore tubing is, however, somewhat undesirable fromthe standpoint that the pressure samples which are conveyed from thepneumotach may be damped or distorted as they travel through the tubing.Consequently, it is often necessary to screen the sensors andindividually balance the internal pneumatics of the monitor to ensureaccurate measurement of airway pressure and, thus, to provide anacceptable level of clinical performance under conditions such as thosetypically encountered with monitored patients (i.e., low ventilatorycompliance).

Additionally, the use of flow sensors with tubing in clinicalenvironments, such as critical and intensive care where high humidity isoften the norm, leads to the condensation of moisture in the pressuretransmission tubing, whether or not the pressure transmission tubing orany portion of the respiratory conduit is heated. One result ofcondensation is a damping and distortion of respiratory samples, or thepressure “signals”, that propagate down the pressure transmission tubes.Typically, pressure transmission tubes are periodically purged with airfrom a compressed gas source or a pump in order to reduce the adverseeffects of condensate on pressure and flow measurements, which createsadditional work for health care personnel and, therefore, is a somewhatundesirable practice. Additionally, accidental or intentionaldisconnection of the tubing from the monitor may cause condensate oreven sputum to flow into the pressure transmission tubes and potentiallycontaminate the monitor.

Further, the lengthy tubing of conventional differential pressure flowsensors is typically discarded after use, resulting in a significantamount of plastic waste. Accordingly, employing such tubing as asingle-use element of a differential pressure flow sensor is costly.

Reuse of pressure transmission tubing is also typically contrary tomanufacturer recommendations due to the potential for contamination ofthe pressure transducer, as well as the potential (although notsignificant) extubation hazard posed thereby in the clinicalenvironment. Nonetheless, such tubing is often reused, particularlyoutside of the United States, as a cost-saving measure.

The inventors are not aware of a differential pressure flow sensor thatlacks pressure transmission tubes extending between the pneumotach andmonitor thereof, or of a differential flow sensor that includes atransducer, that is configured to be carried upon a respiratory conduitthat communicates with the airway of an individual.

SUMMARY OF THE INVENTION

The present invention includes a portable pressure transducer which isconfigured to be positioned on or proximate to a respiratory conduitthat is, in turn, configured to communicate with the airway of anindividual. The present invention also includes a pneumotach with whichthe portable pressure transducer may be coupled to facilitatecommunication between the individual's airway and the portable pressuretransducer. When the portable pressure transducer and pneumotach areassembled with one another, respiratory gas samples may be transportedfrom the respiratory conduit to the portable pressure transducer whilemaintaining a fluid-tight seal between the portable pressure transducerand the pneumotach. In addition, the present invention includes methodsfor obtaining measurements of respiratory pressures, flows, volumes, andother respiratory and blood gas parameters.

A pneumotach that incorporates teachings of the present invention maybeembodied as a so-called “airway adapter” and includes a primary conduit,which aligns with the primary pathway through a respiratory conduit,such as a breathing circuit or a nasal canula, that is configured tocommunicate with the airway of an individual. In addition to the primaryconduit, the pneumotach includes two pressure ports that communicatewith the primary conduit and that are positioned at opposite sides of anobstruction located along and partially blocking the primary conduit, aswell as other components that are typically associated with pressure orflow sensing apparatus. The pressure ports are configured to communicatewith sample conduits of a portable pressure transducer upon coupling ofthe portable pressure transducer to the pneumotach. The location of eachpressure port to which the sample conduits couple may include aresealing material or a so-called “self-healing” material, which sealsthe pressure ports prior to coupling of the sample conduits of theportable pressure transducer thereto and reseals upon uncoupling of thesample conduits of the portable pressure transducer from the pressureports of the pneumotach.

The pneumotach may optionally include additional functionality, such asfor monitoring the amounts of one or more gases or vaporized substancesin the respiration of an individual. By way of example only, thepneumotach may include one or more windows and be configured to have anoptical transducer of an infrared sensor or a luminescence-quenchingtype sensor coupled thereto.

A portable pressure transducer according to the present invention isconfigured to be operatively coupled to a pneumotach of the inventionand, thus, may be carried upon a respiratory conduit. Either thepressure ports of the pneumotach or those of the sample conduits of theportable pressure transducer are substantially larger than the other soas to facilitate the formation and maintenance of a fluid-tight (e.g.,airtight) seal without requiring precise alignment between all(typically two) of the pressure ports and their corresponding sampleconduits. By configuring the pneumotach in this manner, widemanufacturing tolerances may be used, which decreases the cost of thepneumotach, thereby making the pneumotach more amenable to singlepatient use (i.e., disposability). Further, configuring one of thepneumotach and the portable pressure transducer with relatively loosetolerances facilitates the relatively easy assembly of these twostructures. In addition to sample conduits that align with the pressureports of the pneumotach, the portable pressure transducer may includevalves that direct the flow of an individual's respiration therethroughand also includes one or more pressure sensors by which an individual'srespiratory pressure is measured.

Respiratory measurements obtained with a respiratory monitoring systemthat includes a pneumotach and a portable pressure transducer accordingto the present invention may be used, as known in the art, to determinevarious pressure and flow parameters relating to the respiration of anindividual, as well as other respiratory profile parameters that arebased in part on the pressure or flow of the individual's respiration.Accordingly, methods of using the pneumotach and portable pressuretransducer of the present invention are also within the scope thereof.

Other features and advantages of the present invention will becomeapparent to those of ordinary skill in the art through consideration ofthe ensuing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which depict various aspects of exemplary embodimentsof the present invention:

FIG. 1 is a schematic representation of a respiratory conduit thatcommunicates with an airway of an individual and which has a pneumotachand portable pressure transducer of the present invention operativelycoupled thereto;

FIG. 2 is a cross-sectional representation of an exemplary embodiment ofa pneumotach, in the form of an airway adapter, that incorporatesteachings of the present invention;

FIG. 3 is a cross-sectional representation of a variation of thepneumotach depicted in FIG. 2;

FIG. 4 is a cross-sectional representation of an exemplary embodiment ofa portable pressure transducer according to the present invention, whichis configured to be assembled with the pneumotach shown in FIG. 2;

FIG. 5 is a side cross-sectional assembly view of the pneumotach of FIG.2 assembled with the portable pressure transducer of FIG. 4;

FIG. 5A is a side cross-sectional assembly view of another embodiment ofpneumotach and complementary portable pressure transducer according tothe present invention;

FIG. 6 is a side cross-sectional assembly view of another exemplaryembodiment of portable pressure transducer and complementary airwayadapter-type pneumotach according to the present invention;

FIG. 7 is a perspective assembly view of an exemplary embodiment of amulti-function airway adapter, including a pressure sensing component,an infrared sensing component, and a complementary infrared-sensing typetransducer that incorporate teachings of the present invention; and

FIG. 8 is a perspective assembly view of another exemplary embodiment ofa multifunction airway adapter according to the present invention, whichincludes a pressure sensing component, a luminescence-quenching typesensing component, and a complementarily configured transducer of aluminescence-quenching type sensor.

DETAILED DESCRIPTION

With reference to FIG. 1, a respiratory conduit 10 is depicted.Respiratory conduit 10 may comprise a breathing circuit which includesan endotracheal tube, a nasal canula, or any other conduit that isconfigured to communicate with the airway A of an individual I. Asdepicted, one end 12 of respiratory conduit 10 is placed incommunication with airway A, while the other end 14 of respiratoryconduit 10 opens to the atmosphere, a source of gas to be inhaled byindividual I, or a ventilator, as known in the art. Positioned along itslength, respiratory conduit 10 includes at least one airway adapter, inthis case a pneumotach 20, which is a component of a type of pressuresensor. Also shown in FIG. 1 is a portable pressure transducer 50coupled with and in flow communication with pneumotach 20. Portablepressure transducer 50 may, in turn, communicate electronically with acomputer, such as a pressure or flow monitor 100, as known in the art.

Referring now to FIG. 2, the various features of pneumotach 20 may beconfigured as known in the art, for example, like the correspondingfeatures of the differential flow sensors that are described in the '650patent. Among other things, pneumotach 20 includes a primary conduit 22and two pressure ports 24 and 34 that are in flow communication withprimary conduit 22 through apertures 23 and 33. Also, pneumotach 20includes an obstruction 21 to block a portion of the flow of respirationor other gases or gas mixtures along the path of primary conduit 22 andpositioned at least partially between pressure port 24 and pressure port34 to create a pressure differential in the gas flow therebetween.Pneumotach 20 may be formed from an inexpensive, readily mass-produciblematerial, such as an injection moldable plastic, so that pneumotach 20may be marketed as a disposable unit.

Pneumotach 20 is different from the pneumotachs described in the '650patent in that, rather than being configured to be coupled to elongate,flexible conduits, or pressure transmission tubes that transportrespiratory samples to a remotely located pressure transducer forevaluation, pressure ports 24 and 34 are configured to be coupleddirectly to corresponding sample ports 54 and 64 (FIG. 4) (not shown inFIG. 5), respectively, of a complementarily configured pressuretransducer 50 (FIGS. 4 and 5).

As an example, each pressure port 24, 34 may have a sealing element 30,40 covering an opening 25, 35 of that pressure port 24, 34. As anexample and not to limit the scope of the present invention, eachsealing element 30, 40 may comprise a film formed from a material, suchas latex, silicone, or the like, that may be pierced by a member (e.g.,a needle) and maintain a seal at a pressure of up to about 150 cm H₂Oaround the piercing member. Also, the material of each sealing element30, 40 may be formulated to reseal following the removal of a piercingmember therefrom.

Sealing elements 30 and 40 may also hold filters 29 and 39 withinrespective pressure ports 24 and 34 of pneumotach 20. Filters 29 and 39maybe positioned within their respective pressure ports 24 and 34 insuch a way as to avoid disruption (e.g., piercing, tearing, etc.)thereof when a complementarily configured pressure or flow transducer(e.g., portable pressure transducer 50 shown in FIGS. 4 and 5) havingthe aforementioned piercing members is coupled to pneumotach 20. Filters29 and 39 may prevent contamination (e.g., by particulates, moisture,microorganisms, etc.) of a pressure or flow transducer upon coupling ofthe same to pneumotach 20. By preventing contamination of the pressureor flow transducer, filters 29 and 39 facilitate reuse of the pressureor flow transducer without requiring substantial cleaning orsterilization thereof between uses. Accordingly, a pressure or flowtransducer that is complementary to pneumotach 20 may be used withmultiple patients. Filters 29 and 39 may comprise any suitable filtermedium that will facilitate accurate transmission of a pressure waveformfrom pressure ports 24 and 34 into a complementary pressure transducer.Suitable media for filters 29 and 39 include, without limitation,hydrophobic, antimicrobial filter materials, such as those typicallyemployed in respiratory conduits, which may be in the form of felt,particles, or otherwise, as known in the art. While it is desirable thatfilters 29 and 39 not substantially restrict the flow of sampledrespiratory gases through pressure ports 24 and 34, some resistance toairflow is allowable, so long as a sufficient differential pressuresignal may be communicated from pressure ports 24 and 34 of pneumotach20 to a complementarily configured pressure or flow transducer.

Sealing elements 30 and 40 may be secured to their correspondingpressure ports 24 and 34, respectively, by any suitable retention means.By way of example only, an adhesive material which is compatible withthe materials from which both sealing elements 30 and 40 and pressureports 24 and 34 are formed may be placed in appropriate locations tosealingly secure sealing elements 30 and 40 to their correspondingpressure ports 24 and 34.

Alternatively, as depicted in FIG. 3, mechanical retention means, suchas the illustrated rings 32 and 42, may be used to secure sealingelements 30 and 40 to their corresponding pressure ports 24 and 34. Eachring 32, 42 is configured to be positioned peripherally (or, asillustrated, circumferentially) around its corresponding pressure port24, 34. When positioned around a corresponding portion of a pressureport 24, 34, little or no clearance exists between each ring 32, 42 andan adjacent outer surface 26, 36 of the corresponding pressure port 24,34. Once sealing elements 30 and 40 are appropriately positioned overtheir respective openings 25 and 35 of pressure ports 24 and 34,respectively, a ring 32, 42 (which may be formed from heat-shrinkablematerial) or other mechanical retention means may be positioned aroundits corresponding pressure port 24, 34 and a peripheral portion 31, 41of the corresponding sealing element 30, 40 thereon. In this fashion,rings 32 and 42 hold peripheral portions 31 and 41 of the respectivesealing members 30 and 40 in place. As depicted, an outer surface 26, 36of each pressure port 24, 34 may include a peripheral groove 28, 38formed therein, which is configured to receive at least a portion of acorresponding ring 32, 42, as well as a peripheral portion 31, 41 of asealing element 30, 40 positioned between the ring 32, 42 and outersurface 26, 36 of pressure port 24, 34.

Turning now to FIGS. 4 and 5, a portable pressure transducer 50 thatincorporates teachings of the present invention is illustrated. Portablepressure transducer 50 is configured to be at least temporarily coupledto a complementarily configured airway adapter that senses respiratorypressure or flow, such as pneumotach 20.

Portable pressure transducer 50 includes sample ports 54 and 64, whichare positioned in laterally adjacent, spaced-apart relation to oneanother. The distance at which sample ports 54 and 64 are spaced apartfrom one another, as well as their relative orientations, may facilitatecommunication with corresponding pressure ports 24 and 34 of pneumotach20 when portable pressure transducer 50 and pneumotach 20 are assembledwith one another. As depicted, sample ports 54 and 64 are each formed atrespective coupling ends 56 and 66 of sample conduits 55 and 65 ofportable pressure transducer 50. Coupling ends 56 and 66 of sampleconduits 55 and 65 protrude from an outer surface 51 of a housing 52 ofportable pressure transducer 50, while internal portions 58 and 68 ofsample conduits 55 and 65, respectively, are located within housing 52.

In the illustrated example, which in no way limits the scope of thepresent invention, each coupling end 56, 66 of a sample conduit 55, 65comprises a hollow needle, such as an 18, 20, or 25 gaugeinjunction-type needle. When a needle is employed as coupling end 56,66, a smaller circumference (i.e., higher gauge number) may cause lessdamage to a sealing element 30, 40 through which an end of the needle isinserted, which may better facilitate healing or resealing of sealingelement 30, 40 following removal of the needle of coupling end 56, 66therefrom. Additionally, if the outer diameter of each coupling end 56,66 is smaller than the inner diameter of its corresponding pressure port24, 34, precise alignment of coupling ends 56 and 66 with theircorresponding pressure ports 24 and 34 may not be required. The needleof each coupling end 56, 66 is sealingly coupled to a correspondinginternal portion 58, 68 of sample conduit 55, 65 in such a way as towithstand, without substantially leaking, the pressures to whichdifferential pressure transducer 50 will be exposed (e.g., pressures ofup to about 150 mm Hg).

Housing 52 of portable pressure transducer SO may include protectivesleeves 57 and 67 that may extend therefrom and circumferentiallysurround coupling ends 56 and 66, respectively, of sample conduits 55and 65 along substantially their entire external lengths. Protectivesleeves 57 and 67 may also extend beyond their respective coupling ends56 and 66 of sample conduits 55 and 65, respectively, so as to preventcoupling ends 56 and 66 from contacting and, when needles are used, fromscratching or puncturing other structures, the individual beingmonitored, or health care personnel working with or near portablepressure transducer 50. Protective sleeves 57 and 67 are also configuredto receive at least a portion of pressure ports 24 and 34 thatcorrespond to sample ports 54 and 64, respectively.

Internal portions 58 and 68 of sample conduits 55 and 65 independentlycommunicate respiratory gases to a differential pressure sensor 80located within housing 52 of portable pressure transducer 50.Differential pressure sensor 80 senses a pressure differential across atleast a portion of obstruction 21 and transmitted from the airway A ofan individual I (FIG. 1) by pressure ports 24 and 34 and theircorresponding sample conduits 55 and 65, respectively. As differentialpressure sensor 80 is in communication with both sample conduits 55 and65, it is capable of measuring a pressure drop across an element, suchas obstruction 21 positioned in the path of primary conduit 22 ofpneumotach 20 and between pressure ports 24 and 34 with which sampleconduits 55 and 65 respectively communicate. As portable pressuretransducer 50 is to be coupled with a pneumotach 20 which is, in turn,configured to be secured to a respiratory conduit 10 (FIG. 1), it may bedesirable for a differential pressure sensor 80 thereof to be of adesign insensitive to tilting, vibration, movement, or any combinationthereof. It may also be desirable for differential pressure sensor 80 tobe insensitive to, or capable of, compensating for common mode pressurevariations within the respiratory conduit. By way of example and not tolimit the scope of the present invention, differential pressure sensor80 may be configured to measure pressure differences of up to about 4in. H₂O (i.e., about 10 cm H₂O), although a differential pressure sensor80 of portable pressure transducer 50 of the present invention may be ofa type capable of measuring pressure differences of up to about 10 in.H₂O (i.e., about 25 cm H₂O). By way of example only, a dual-chippressure transducer, which includes a bridge circuit array of resistorsand which is capable of monitoring both airway and differentialpressure, may be used as differential pressure sensor 80 of portablepressure transducer 50. An example of such a dual-chip pressuretransducer is the XCX Series transducer manufactured by AllSensorsCorporation of San Jose, Calif.

Differential pressure sensor 80 may communicate signals that arerepresentative of the measured difference in pressure between air orgases within sample conduit 55 and air or gases within sample conduit 65to a processor 102 of a pressure or flow monitor 100, as known in theart (e.g., along a computer communication cable, by wirelesstransmission, such as infrared transmission, etc.). Processor 102, undercontrol of one or more programs in the form of software or firmware, maythen, based on the signals received thereby, employ known principles andalgorithms to calculate respiratory flow. Signal conditioningelectronics 81 of a type known in the art, such as an instrumentationamplifier, may be associated with differential pressure sensor 80, asknown in the art, to amplify the signals that are generated andtransmitted thereby as well as reduce or eliminate noise and othersignal artifacts. Processor 102 may also quantify airway pressure atdifferent points or portions of the monitored individual's respiration,also by known processes.

Sample conduit 55 also communicates with a gauge or ambient pressuresensor 90, which is also in flow communication with the atmosphereexternal to portable pressure transducer 50. Gauge pressure sensor 90may be positioned proximally, in reference to the location of themonitored individual, relative to differential pressure sensor 80. Inthe illustrated example, gauge pressure sensor 90 communicates with theatmosphere by way of a conduit 92 that extends through housing 52 ofportable pressure transducer 50 and that opens to the atmosphere. Asgauge pressure sensor 90 communicates with both the atmosphere (e.g., byway of conduit 92) and the airway A (FIG. 1) of an individual I (by wayof sample conduit 55, as well as other conduits and ports), gaugepressure sensor 90, which may also comprise a differential pressuresensor, may sense differences between atmospheric pressure and airwaypressure. Gauge pressure sensor 90 may be of a type insensitive to oneor more of tilt, vibration, movement, or any combination thereof. It mayalso be desirable for gauge pressure sensor 90 to be insensitive to, orcapable of, compensating for common mode pressure variations within therespiratory conduit. As an example and not by way of limitation, gaugepressure sensor 90 may be capable of sensing pressure differences of upto about 120 mm Hg. By way of example only, an XCX Series, dual-chipdifferential pressure sensor available from AllSensors may be used asgauge pressure sensor 90.

Gauge pressure sensor 90 generates signals representative of suchmeasured pressure and communicates the same to processor 102, which maybe programmed, as known in the art, to consider the differences betweenatmospheric and airway pressure in quantifying the pressure at one ormore particular points or portions of the monitored individual'srespiration, as well as in calculating respiratory flow. These signalsmay be amplified or otherwise modified by signal conditioningelectronics 91, such as an instrumentation amplifier, which isassociated with gauge pressure sensor 90 in a manner known in the art.

Portable pressure transducer 50 may also include a valve 60, 70positioned along each sample conduit 55, 65, between coupling end 56, 66thereof and differential pressure sensor 80 and/or gauge pressure sensor90 (i.e., upstream from sensors 80 and/or 90). Each valve 60, 70controls (i.e., permits or restricts) the flow of respiratory gasesthrough its corresponding sample conduit 55, 65. For example, whenvalves 60 and 70 are both in open positions, respiratory gases may flowtherethrough and, thus, along their respective sample conduits 55 and65. Conversely, when valves 60 and 70 are closed, respiratory gases arerestricted from flowing completely through sample conduits 55 and 65.Exemplary valves that may be used in portable pressure transducer 50include the three-way solenoid valves marketed under the trade nameX-VALVE® by the Pneutronics Division of Parker Hannifin Corporation,which is located in Hollis, N.H., or titanium nickel valves manufacturedby TiNi Alloy Company of San Leandro, Calif. Valves 60 and 70 may beconfigured to communicate with a control device, such as processor 102of monitor 100 or a processor of a separate computer (not shown)associated with monitor 100, which is programmed to actuate valves 60and 70 and, thus, to control the flow of respiratory gases throughsample conduits 55 and 65. Such communication may be effected wirelessly(e.g., by infrared signals or other known, suitable wavelengths ofelectromagnetic radiation) or via wires or cables.

Valves 60 and 70 may be closed, or placed in a “zeroing” position, tofacilitate the measurement of atmospheric pressure only and, thus,permit gauge pressure sensor 90 and differential pressure sensor 80 togenerate so-called “baseline” pressure signals. Accordingly, byperiodically reestablishing baseline pressure, any susceptibility thatdifferential pressure sensor 80 or gauge pressure sensor 90 may exhibitto experiencing “baseline drift” may be counteracted.

Alternately, when valves 60 and 70 are both in open, or “measuring,”positions, respiratory samples may flow through sample conduits 55 and65 and to differential pressure sensor 80 and gauge pressure sensor 90,thereby facilitating measurement of airway pressure. The pressuremeasurements that are obtained with valves 55 and 65 in open positionsmay be corrected by considering the baseline pressure measured by eachof differential pressure sensor 80 and gauge pressure sensor 90. Forexample, the baseline pressure of each sensor 80, 90 may be subtractedfrom the pressure measurement subsequently obtained by that sensor 80,90.

Portable pressure transducer 50 may also include a power provisionelement 75, such as an interconnection (e.g., a wire or cable) to aremote power source or an internal power source (e.g., a battery) forsupplying power to valves 60 and 70, differential pressure sensor 80,gauge pressure sensor 90, and other power-consuming elements of portablepressure transducer 50.

Housing 52 of portable pressure transducer 50 may be configured toprevent moisture-sensitive components thereof, such as differentialpressure sensor 80 and gauge pressure sensor 90, from being exposed tomoisture (e.g., from humidity, sources of fluid, etc.). In addition,filters 29 and 39 of pneumotach 20 may prevent moisture from coming intocontact with these moisture-sensitive components of portable pressuretransducer 50. A similar, optional filter 94 may likewise be positionedalong conduit 92 to prevent exposure of gauge pressure sensor 90 tomoisture from the environment external to housing 52.

As an alternative to the embodiments of pneumotach 20 and portablepressure transducer 50 shown in and described with reference to FIGS.2-5, various features of the pressure ports of the pneumotach and of thecoupling ends of the sample conduits of the portable pressure transducermay be reversed, as depicted in FIG. 5A. As shown, a pneumotach 20′ mayinclude pressure ports 24′ and 34′ with hollow needles 27′ and 37′protruding therefrom. Needles 27′ and 37′ are configured to be coupledwith coupling ends 56′ and 66′, respectively, of corresponding sampleconduits 55′ and 65′ of a complementarily configured portable pressuretransducer 50′. In particular, as the outer diameter of each needle 27′,37′ is significantly smaller than the inner diameter of a coupling end56′, 66′ of its corresponding sample conduit 55′, 65′ over which aprotective sleeve 57′, 67′, or sealing element is positioned, eachneedle 27′, 37′ is configured to roughly align with and temporarilypuncture a sealing element 57′, 67′ on a coupling end 56′, 66′ of itscorresponding sample conduit 55′, 65′. Needles 27′ and 37′ may compriseany hollow, injection-type needle with a small circumference (e.g., an18, 20, or 25 gauge needle) and a tip which will readily pierce sealingelement 57′, 67′. Sealing elements 57′ and 67′ may be formed from anymaterial that will form an adequate seal (e.g., a seal which may bemaintained at pressures of up to about 150 mm Hg) around the outersurface of a needle 27′, 37′, while substantially resealing upon removalof a needle 27′, 37′ therefrom. Exemplary materials that may be used assealing elements 57′ and 67′ include, without limitation, films oflatex, silicon, and other relatively soft, resilient elastomericmaterials.

In another exemplary embodiment of both a pneumotach and portablepressure transducer that incorporate teachings of the present invention,corresponding elements of these apparatus are configured to matinglyengage one another upon assembly of the pneumotach and portable pressuretransducer with one another. These embodiments of pneumotach 20″ andportable pressure transducer 50″, which are depicted in FIG. 6, requiremore precise, or finer, alignment between corresponding features than dothe previously described embodiments.

Pneumotach 20″ differs from pneumotach 20 (FIGS. 2, 3, and 5) in thatpressure ports 24″ and 34″ thereof include coupling ends 27″ and 37″(female members in the depicted example) that are configured to matinglyengage (e.g., by way of an interference fit, complementary threadedjoints (not shown), or otherwise) complementary coupling ends 56″ and66″ (male members in the depicted example) of corresponding sampleconduits 55″ and 65″, respectively, of portable pressure transducer 50″.A filter 29″, 39″ extends across each pressure port 24″, 34″ to preventmicroorganisms, moisture, and other contaminants from passingtherethrough and into sample conduits 55″ and 65″ of portable pressuretransducer 50″. Sample conduits 55″ and 65″ may likewise have filters59″ and 69″ extending thereacross to prevent contamination of the otherelements of portable pressure transducer 50″. Filters 29″, 39″, 59″, and69″ may each comprise any suitable filter medium that will facilitateaccurate transmission of a pressure waveform from pressure ports 24″ and34″ into corresponding sample conduits 55″ and 65″, respectively.Suitable media for filters 29″, 39″, 59″, and 69″ include, withoutlimitation, hydrophobic, antimicrobial filter materials, such as thosetypically employed in respiratory conduits, which may be in the form offelt, particles, or otherwise, as known in the art. Other features ofpneumotach 20″ and portable pressure transducer 50″ are substantiallythe same as those which are described above with respect to pneumotach20, in reference to FIGS. 2, 3, and 5, and portable pressure transducer50, in reference to FIGS. 4 and 5.

Optionally, an airway adapter and complementary transducer thatincorporate teachings of the present invention may be configured formultiple diagnostic functions. By way of example only, in addition tofunctioning as a pneumotach, an airway adapter of the present inventionmay also include a material sensing element, such as one or both of aninfrared sensor, as described in the U.S. Pat. Nos. 4,859,858 and4,859,859, both of which issued to Knodle et al. on Aug. 22, 1989(hereinafter respectively “the '858 patent” and “the '859 patent”), andU.S. Pat. No. 5,153,436, issued to Apperson et al. on Oct. 6, 1992(hereinafter “the '436 patent”), the disclosures of each of which arehereby incorporated by this reference in their entireties, and aluminescence quenching-type sensor, as described in U.S. Pat. No.6,325,978, issued to Labuda et al. on Dec. 4, 2001 (hereinafter “the'978 patent), the disclosure of which is hereby incorporated herein bythis reference in its entirety. A complementary transducer would, ofcourse, act as a pressure transducer and one or both of an infraredsensing-type transducer and luminescence excitation and detectiontransducer.

FIG. 7 schematically depicts an example of an assembly including amulti-function airway adapter 120 and a transducer 150 of aninfrared-type sensor that may be used therewith. Airway adapter 120 hasthe features of pneumotach 20 described previously herein with referenceto FIGS. 2, 3, and 5, to which a complementarily configured portablepressure transducer 50 (FIGS. 4 and 5) may be secured. In addition,airway adapter 120 includes a pair of opposed windows 122, only one ofwhich is shown, which facilitates the transmission of infrared radiationthrough primary conduit 22 of airway adapter 120 and any gases orvaporized materials therein, as well as the detection of infraredradiation that has not been absorbed by windows 122 or gases or othermaterials within primary conduit 22. Airway adapter 120 also includes aseating element 126, which is configured to ensure that thecomplementarily configured transducer 150 seats properly, i.e., in theproper orientation, when airway adapter 120 and transducer 150 areassembled with one another. When properly positioned on airway adapter120, transducer 150 preferably does not interfere with the assembly of aportable pressure transducer 50 (FIGS. 4 and 5) with airway adapter 120.Transducer 150 may include each of the elements of an infraredmonitoring transducer, as described in the '858, '859, and '436 patents.Among other things, an infrared source 152 and at least one infrareddetector 154 may be positioned so as to respectively direct infraredradiation into one window 122 and detect infrared radiation through theother window (not shown). Operation of infrared source 152 and infrareddetector 154 may be controlled and monitored, as known in the art, by aprocessor of a suitable monitoring apparatus (e.g., processor 102 ofmonitor 100 shown in FIG. 5) with which infrared source 152 and infrareddetector 154 communicate electronically, as known in the art.

Referring now to FIG. 8, an alternative embodiment of multifunctionairway adapter 120′ and complementary transducer 150′ of aluminescence-quenching type sensor are depicted. Airway adapter 120′includes a pneumotach, such as pneumotach 20 described previously hereinwith reference to FIGS. 2, 3, and 5. Airway adapter 120′ also includes aluminescence-quenching portion 130, which facilitates monitoring of oneor more substances (e.g., oxygen) in respiratory gases by way of knownluminescence quenching techniques, as described in the '978 patent.

Luminescence-quenching portion 130 of airway adapter 120′ includes aquantity of luminescable material 132, which may be carried by a supportmembrane 134, within a primary conduit 22 of pneumotach 20. Theluminescence of luminescable material 132 is quenched to a degreeindicative of an amount of an analyzed gas (e.g., oxygen, nitrous oxide,etc.) or vaporized material (e.g., one or more anesthetic agents) in agas mixture (e.g., respiration of an individual) to which luminescablematerial 132 is exposed. Airway adapter 120′ also includes a window 122′through which at least a portion of luminescable material 132 may beexcited into a luminescent state and through which light or otherelectromagnetic radiation emitted from luminescable material 132 may bedetected. Examples of luminescable materials 132 and support membranes134, as well as their positioning within airway adapter 120′ relative toa window 122′ thereof, and examples of materials from which window 122′may be formed are more fully described in the '978 patent.

Transducer 150′ includes at least a source 162 of electromagneticradiation of one or more wavelengths that will excite luminescablematerial 132 into a luminescent state, as well as a detector 164 forsensing electromagnetic radiation emitted by luminescable material 132.Source 162 and detector 164 are positioned and oriented within a housing155′ of transducer 150′ in such a way that both source 162 and detector164 are oriented toward window 122′ of airway adapter 120′ andluminescable material 132 within airway adapter 120′ when transducer150′ and airway adapter 120′ are assembled with one another. Thespecifics of source 162, detector 164, and other elements of transducer150′, including control and monitoring of their operation by a processorof a suitable monitoring apparatus (e.g., processor 102 of monitor 100shown in FIG. 5) and transmission of signals from detector 164 to such aprocessor are more fully described in the '978 patent.

Airway adapter 120′ may also include a seating element 126, which, alongwith a complementary element or portion 156 of transducer 150′, isconfigured to ensure that appropriate elements of airway adapter 120′and transducer 150′, such as window 122′ of airway adapter 120′ andsource 162 and detector 164 of transducer 150′ are in adequate alignmentwith one another upon assembly of airway adapter 120′ and transducer150′. When transducer 150′ is properly positioned on airway adapter120′, transducer 150′ preferably does not interfere with the assembly ordisassembly of portable pressure transducer 50 (FIGS. 4 and 5) with itsrespective luminescence-quenching portion 130 of airway adapter 120′.

In addition to the material sensing functions of transducers 150 and150′ depicted in FIGS. 7 and 8, respectively, transducers 150 and 150′may be equipped with pressure sensing portions which include thefeatures of a portable pressure transducer of the present invention(e.g., portable pressure transducer 50 depicted in FIGS. 4 and 5).

Once signals that correspond to pressure measurements obtained by use ofa pneumotach (e.g., pneumotach 20 shown in FIG. 5) and complementaryportable pressure transducer (e.g., portable pressure transducer 50shown in FIG. 5) of the present invention have been transmitted to aprocessor of a pressure monitor (e.g., processor 102 of pressure monitor100 shown in FIG. 5), known techniques and algorithms may be employed tocalculate various flow, volume, respiratory mechanics, and otherrespiratory parameters, as well as measurements of blood flow and bloodgases.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some exemplary embodiments.Similarly, other embodiments of the invention may be devised which donot depart from the spirit or scope of the present invention. Featuresfrom different embodiments may be employed in combination. The scope ofthe invention is, therefore, indicated and limited only by the appendedclaims and their legal equivalents, rather than by the foregoingdescription. All additions, deletions, and modifications to theinvention, as disclosed herein, which fall within the meaning and scopeof the claims are to be embraced thereby.

What is claimed is:
 1. A respiratory pressure sensing system,comprising: (a) a pneumotach configured to be positioned along arespiratory conduit, the pneumotach comprising: (1) a pneumotachhousing, (2) a primary conduit defined in the pneumotach housing, (3) afirst pressure port and a second port, wherein the first pressure portand the second pressure port are defined in the pneumotach housing influid communication with the primary conduit, and (4) a pressuretransducer coupling portion disposed on the pneumotach housing; and (b)a pressure transducer configured to be removably coupled with thepneumotach, the pressure transducer comprising: (1) a pressuretransducer housing, (2) a pneumotach coupling portion disposed on thepressure transducer housing and configured to selectively and removablyengage the pressure transducer coupling portion to attach the pressuretransducer housing to the pneumotach housing, (3) a first pressuresensor disposed in the housing, and (4) a first sample conduit and asecond sample conduit, wherein the first sample conduit and the secondsample conduit each includes a first portion disposed in the housing andcoupled to the first pressure sensor, and a second portion adapted tocooperate with an associated pressure port of the pneumotach so as tocommunicate a respiratory sample from the primary conduit of thepneumotach to the first pressure sensor responsive to the pressuretransducer housing being coupled to the pneumotach housing.
 2. Thesystem of claim 1, wherein the pneumotach further includes a flowrestricting element disposed in at least a portion of the primaryconduit, and wherein the first and the second pressure ports arepositioned on opposite sides of the flow restricting element.
 3. Thesystem of claim 1, wherein the second portion of the first conduit andthe second portion of the second conduit is defined by a portion of thehousing.
 4. The system of claim 3, wherein the portion of the housingdefining the second portion of the first conduit and defining the secondportion of the second conduit each includes a piercing portion.
 5. Thesystem of claim 1, wherein the first pressure sensor comprises adifferential pressure sensor in communication with the first and thesecond sample conduits.
 6. The system of claim 5, wherein the pressuretransducer further includes a second pressure sensor having a firstportion in communication with at least one of the first and the secondpressure ports and a second portion in communication with an environmentexternal to the pressure transducer.
 7. The system of claim 1, whereinthe first pressure port includes a first opening and the second pressureport includes a second opening, and wherein the pneumotach furtherincludes a first sealing member covering the first opening and a secondsealing member covering the second opening.
 8. The system of claim 1,wherein the first sampling conduit includes a first opening and thesecond sampling conduit includes a second opening, and wherein thepressure transducer further comprises a first sealing portion coveringthe first opening and a second sealing portion covering the secondopening.
 9. The system of claim 8, wherein the first sealing portion andthe second sealing portion are defined by a common sealing member. 10.The system of claim 1, wherein the second portion of the first sampleconduit comprises a first piercing member, and wherein the secondportion of the second sample conduit comprises a second piercing member.11. The system of claim 1, wherein the pneumotach further comprises afirst hollow protruding portion extending from the pneumotach housing atthe first pressure port and a second hollow protruding portion extendingfrom the pneumotach housing at the second pressure port.
 12. The systemof claim 11, wherein the first hollow protruding portion includes afirst piercing portion disposed at an end thereof, and wherein thesecond hollow protruding portion includes a second piercing portiondisposed at an end thereof.
 13. The system of claim 1, furthercomprising a first valve disposed in the first sample conduit and asecond valve disposed in the second sample conduit.
 14. The system ofclaim 1, further comprising a monitor in communication with the firstpressure sensor, wherein the monitor is programmed to calculate arespiratory pressure parameter, a respiratory flow parameter, arespiratory volume parameter, a blood gas parameter, a blood flowparameter, or any combination thereof based at least partially on asignal from the first pressure sensor.
 15. A method for monitoring aparameter associated with respiration of a patient, comprising: (a)providing a respiratory circuit in fluid communication with an airway ofa patient; (b) providing a pneumotach at a first location along therespiratory conduit, the pneumotach comprising: (1) a pneumotachhousing, (2) a primary conduit defined in the pneumotach housing, (3) afirst pressure port and a second port, wherein the first pressure portand the second pressure port are defined in the pneumotach housing influid communication with the primary conduit, and (4) a pressuretransducer coupling portion disposed on the pneumotach housing; and (c)providing a pressure transducer comprising: (1) a pressure transducerhousing, (2) a pneumotach coupling portion disposed on the pressuretransducer housing and configured to selectively and removably engagethe pressure transducer coupling portion to attach the pressuretransducer housing to the pneumotach housing, (3) a first pressuresensor disposed in the housing, and (4) a first sample conduit and asecond sample conduit, wherein the first sample conduit and the secondsample conduit each includes a first portion disposed in the housing andcoupled to the first pressure sensor, and a second portion adapted tocooperate with an associated pressure port of the pneumotach so as tocommunicate a respiratory sample from the primary conduit of thepneumotach to the first pressure sensor responsive to the pressuretransducer housing being coupled to the pneumotach housing; and (d)attaching the pressure transducer to the pneumotach by engaging thepneumotach coupling portion with the pressure transducer couplingportion.
 16. The method of claim 15, wherein attaching the pressuretransducer to the pneumotach includes providing a fluid communicationbetween the first pressure port and the first sample conduit andproviding a fluid communication between the second pressure port and thesecond sample conduit.
 17. The method of claim 16, wherein providing afluid communication between the first pressure port and the first sampleconduit includes piercing a first seal disposed on the first pressureport with the second portion of the first sample conduit, and whereinproviding a fluid communication between the second pressure port and thesecond sample conduit includes piercing a second seal disposed on thesecond pressure port with the second portion of the second sampleconduit.
 18. The method of claim 16, wherein providing a fluidcommunication between the first pressure port and the first sampleconduit includes piercing a first seal disposed over the second portionof the first sample conduit with a first hollow protruding portionextending from the pneumotach housing at the first pressure port, andwherein providing a fluid communication between the second pressure portand the second sample conduit includes piercing a second seal disposedover the second portion of the second sample conduit with a secondhollow protruding portion extending from the pneumotach housing at thesecond pressure port.
 19. The method of claim 15, further comprising (e)disassembling the pressure transducer from the pneumotach.